Compound transmission systems comprising multi-speed main transmission sections connected in series with one or more multi-speed auxiliary transmissions sections, usually the range, splitter, or a combined range/splitter type are well known in the prior art. The auxiliary sections are usually input and/or output auxiliary transmission sections but may also be multi-speed drive axles, transfer cases or the like. Examples of such compound systems may be seen by reference to U.S. Pat. Nos. 3,648,546; 3,799,022; 4,455,883; 4,527,497; 4,754,655; 4,901,600 and 5,000,060, the disclosures of which are incorporated herein by reference.
The auxiliary transmission sections commonly employ actuating devices for effecting the particular change gear ratio desired by selectively moving range clutch assemblies and/or splitter clutch assemblies between first and second positions commonly by means of fluid operated range piston assemblies and fluid operated splitter piston assemblies mounted on the auxiliary section housing.
In many instances, a comparatively large force is required to selectively move the range clutch assembly between the two positions to effect the particular change gear ratio desired. In such instances, as the regulated/filtered on-board air pressure is usually limited to pressurization (usually 60-80 psi), it has been heretofore necessary to mount the range piston assembly on the exterior of the auxiliary section housing because of the large diameter pressurized fluid chamber required to provide the necessary force against the piston head. As such, the exterior mounting of the range piston assembly exposes it to contamination and potential damage as well as requiring an opening in the housing itself to enable operative connection to the range clutch assembly.
The present invention solves the exposure problem by replacing the conventional singular pressurized fluid chamber piston assembly heretofor used with a range piston assembly of diminished size able to fit within and be protectively enclosed by the auxiliary section housing by employing a plurality of tandem pressurized fluid chambers cumulatively able to provide the amount of force required to selectively move the range clutch assembly between the first and second positions.
Tandem fluid operated pistons have been known for many years as a means of magnifying force available from a singular pressurized fluid pressure source. Examples of such can be seen in U.S. Pat. Nos. 2,245,501 and 4,005,598, the disclosures of which are incorporated herein by reference. The present invention however, employs such knowledge not to magnify a given force, but rather to provide a reduction in size yet able to provide substantially the same force heretofor required to selectively move the range clutch assembly between the first and second positions.